Add private fields to proposal components

[froger]

🎩 What? Why?
This PR gives admins the ability to define as many private fields as are considered necessary, and also delete the fields defined as private in the proposals component at the end of the process, without deleting the rest of the content proposal or the authorship.

📌 Related Issues
Same as #307, but using a branch where decidim-awesome contributors can make updates.
Related to #?
Fixes # Add private fields to the Proposals component

Testing

📷 Screenshots

proposal private fields menu

Disclosure for private fields

♥️ Thank you!

[codecov]

Codecov Report

Attention: Patch coverage is 53.93586% with 158 lines in your changes missing coverage. Please review.

Project coverage is 67.87%. Comparing base (a851688) to head (457bd45).
Report is 60 commits behind head on develop.

Files	Patch %	Lines
...m_awesome/proposals/proposal_serializer_methods.rb	28.94%	27 Missing ⚠️
...m_awesome/proposals/application_helper_override.rb	8.69%	21 Missing ⚠️
...decidim_awesome/add_proposal_type_custom_fields.rb	43.33%	17 Missing ⚠️
...cidim/decidim_awesome/has_proposal_extra_fields.rb	36.00%	16 Missing ⚠️
...forms/decidim/decidim_awesome/admin/config_form.rb	17.64%	14 Missing ⚠️
...idim/decidim_awesome/amendments_helper_override.rb	8.33%	11 Missing ⚠️
...awesome/api/types/translated_custom_fields_type.rb	64.00%	9 Missing ⚠️
..._awesome/proposals/proposal_serializer_override.rb	57.89%	8 Missing ⚠️
lib/decidim/decidim_awesome/engine.rb	76.47%	8 Missing ⚠️
...wesome/proposals/admin/update_proposal_override.rb	78.57%	3 Missing ⚠️
... and 13 more

❗ There is a different number of reports uploaded between BASE (a851688) and HEAD (457bd45). Click for more details.

HEAD has 6 uploads less than BASE

Flag	BASE (a851688)	HEAD (457bd45)
	8	2

Additional details and impacted files

@@             Coverage Diff              @@
##           develop     #314       +/-   ##
============================================
- Coverage    96.02%   67.87%   -28.15%     
============================================
  Files           97       75       -22     
  Lines         2440     2014      -426     
============================================
- Hits          2343     1367      -976     
- Misses          97      647      +550     

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